The invention is basically concerned with composite cans or containers utilizing tubular bodies of at least one, and normally multiple, plies of cardboard, paperboard, or the like spirally or convolutely wound to define a rigid self-sustaining body to which metal end caps are seamed.
Such containers have found wide acceptance, and, as the various problems of moisture impermeability, air tightness, and the like are being solved, are increasingly used as a highly desirable substitute for the more conventional metal container or can.
However, one significant problem which still exists with regard to the use of composite cans, particularly those with what might be considered heavy walls, that is walls with a thickness of 0.030 inch or greater, is the substantial difficulty encountered in opening such containers using the conventional manual or electric can openers found in substantially every home. This problem has heretofore been recognized, and is in fact discussed in great detail in U.S. Pat. No. 3,397,809, issued to Donald H. Ellerbrock on Aug. 20, 1968.
Basically, fiber composite can body walls are softer, more compressible and thicker than the metal walls used in conventional metal cans. Thus, upon seaming a metal lid to a composite body, the resultant seam or bead is both thicker and softer or more readily compressible than the same seam on a metal can. While the conventional can opener, made to accommodate conventional metal cans, can be canted to engage the thicker seam or bead on a composite can, this frequently causes an improper and ineffective engagement of the cutting blade and/or drive wheel of the can opener. Attempts to sufficiently engage the can opener with a composite container seam for a proper opening of the container results, in many instances, in an unsightly and destructive tearing of the outer or label ply of the container. Finally, even when fully engaged with the seam or bead, effecting sufficient clamping of the can opener to the container to pierce the cap and progressively sever the cap from the bead as the can opener is driven thereabout frequently results in merely crushing the bead. Such crushing of the bead results from an inability of the bead or seam to sustain the normal forces required to drive the opener in that the bead or seam includes the interposed relatively soft and compressible composite material of the body end, as opposed to the substantially stronger solid metal seam encountered in metal containers. Ellerbrock proposes a solution to the problem of accommodating a composite container to a conventional can opener by modifying the metal cap or end by providing a pre-weakened circumferential area immediately inward of the bead or seam to reduce the resistance to cutting and thus the driving force required by the driving wheel. While the Ellerbrock proposal may facilitate the opening of composite containers, the retained thick seam still requires substantial canting of the opener, and an accompanying rather severe scuffing or cutting of the body wall immediately below the bead.